CFC (chlorofluorocarbon) and HCFC (hydrochlorofluorocarbon), which have been conventionally used as refrigerants for refrigeration equipment, have been subject to regulation due to the problem of recent ozone depletion, and HFC (hydrofluorocarbon) has come to be used as a refrigerant instead of them.
Among HFC refrigerants, HFC-134a, R407C, and R410A are normally used as refrigerants for car air-conditioners, coolerators, or room air-conditioner. Although the ozone depletion potential (ODP) of these HFC refrigerant is zero, these come to be subject to regulation, because the global warming potential (GWP) thereof is high. While difluoromethane has been studied as one of alternate candidates of these refrigerants, difluoromethane has the following problems: the global warming potential thereof is not sufficiently low; the boiling point thereof is so low that thermodynamic characteristics cannot be applied to a current refrigeration system directly; and difluoromethane is not easily compatible with lubricating oils (refrigerating machine oils) used for conventional HFC refrigerants, such as polyol esters and polyvinyl ethers. On the other hand, unsaturated hydrofluorocarbons have been proposed to be used as a refrigerant due to the following reasons; both of its ODP and GWP are very low; unsaturated hydrofluorocarbons are non-flammable depending on structures; and in particular with respect to HFO-1234yf, thermodynamic characteristics as measures of refrigerant performances are comparable with or better than those of HFC-134a (Patent Literatures 1 to 3).
In addition, a working medium consisting of 80% by mass or more of one or more first components selected from 1,1-difluoroethane (HFC-152a), 1,1,1-trifluoro-2-monofluoroethane (HEC-134a) and 1,1,1-trifluoro-2,2-difluoroethane (HFC-125) as first components, and 20% by mass or less of carbon dioxide (R744) as a second component has been proposed (Patent Literature 4).
Hydrocarbons such as isobutane (R600a) and propane (R290) that are flammable, in which the ODP is 0 and the GWP is as extremely low as about 3, have also been studied (Patent Literatures 5 to 7).